The present invention relates to fluid coupling devices of the type including temperature responsive bimetal elements, and more particularly, to a clip member for mounting the free end of the element, and the associated method of assembly.
Fluid coupling devices of the type to which the present invention relates are now well-known in the art and may be better understood by reference to U.S. Pat. No. 3,055,473, assigned to the assignee of the present invention. Although the present invention may be useful with many types and configurations of temperature responsive fluid couplings, it is especially advantageous on those to be used with vehicle radiator cooling fans, and will be described in connection therewith.
A typical fluid coupling device includes an output coupling member and a cover member cooperating to define a fluid chamber. The device includes a valve plate disposed to separate the fluid chamber into a reservoir and an operating chamber. An input coupling member is rotatably disposed within the operating chamber and the device includes valve means operable to control the flow of fluid between the reservoir and the operating chamber. The valve means includes a valve shaft extending outwardly through the cover means and being rotatable relative thereto. The rotational position of the valve shaft and the valve is controlled by a temperature responsive bimetal element having a first end portion connected to the valve shaft and a second end portion fixed relation to the cover means.
As is well-known to those skilled in the art, one of the primary reasons for using a viscous fluid coupling to drive a radiator cooling fan, rather than the conventional direct drive, is to save engine horsepower. This is accomplished by the fluid coupling becoming "disengaged" when operation of the fan is not needed for cooling of the engine. Accordingly, viscous fluid couplings have been used for many years on the larger six-cylinder and eight-cylinder engines (truck and automotive), where the potential horsepower savings are greatest. More recently, the desire to minimize wasted power on all engines has led to the use of viscous fluid couplings even on four-cylinder engines.
A problem which has arisen in connection with the use of viscous fluid couplings on four-cylinder engines relates to the greater vibration inherent in four-cylinder engines. The engine vibration is transmitted to the fluid coupling and typically, the result is excessive wear between the bimetal element and the shaft and between the bimetal element and its mounting bracket. If excessive wear occurs at either of these locations, there may be a substantial change in the temperature at which the coupling engages and/or disengages, causing unsatisfactory operation of the device.
If the wear becomes really excessive, especially between the bimetal coil and the shaft, the coil may become completely detached from the device, with the result that the device will no longer be temperature responsive, but will remain either engaged or disengaged, whichever was the condition of the device at the time that the coil became detached.
The apparently obvious solution to the above-described problem would seem to be to provide a more rigid mounting of the free end of the coil, relative to the cover of the coupling. However, it was found during the development leading to the present invention that gripping the free end of the coil regidly enough to prevent the coil from being vibrated loose would generally result in the coil being fractured adjacent the point at which it was being rigidly gripped.
Even before breakage of the coil would occur, it was found that any of the obvious methods of rigidly mounting the free end of the coil would adversely affect the performance of the device by inducing high hysteresis. Hysteresis will be described in greater detail subsequently, but briefly, it occurs when improper location or alignment of the coil, shaft, or valve results in frictional drag on the shaft or valve. This drag causes the device to remain engaged until the temperature is substantially below the engagement temperature, wasting engine horsepower and resulting in excessive noise of operation.